DE2727052C2 - Process for purifying high solids clay suspensions - Google Patents

Description

The invention relates to a method for cleaning clay suspensions with a high solids content r>

Naturally occurring clays such as B. Bentonite, usually contain accompanying minerals, their grain size mostly exceeds that of the clay particles and which are also generally harder than the clay particles. With these Gfobteilchen handeil it see for example wi around quartz, mica, feldspar, calcite, dolomite, pyrite, hematitus etc.

Due to their hardness, these coarse fractions can only be cut with great difficulty by dry and wet grinding crush. Also a separation by dry TV> or wet sieving only leads to the desired success down to a certain grain size of the coarse fractions.

When trying to separate the coarse parts of bentonite suspensions in a hydrocyclone, the applicant has found that as a result of the inner-crystalline swelling and division of the clay mineral Montmorillonite the viscosity of clay suspensions with a high solids content increased so much that one Separation of the coarse fractions was hindered. The centrifugal acceleration and the Sink speed of the particles, so that the required pump pressure squared with increasing viscosity rise.

To avoid these difficulties it was necessary to dilute the clay suspensions very much, whereby the subsequent work-up was made more difficult and the profitability was impaired.

It is therefore the object of the invention to develop a method in which bentonite suspensions are also used with a high solids content can be cleaned of ob-components.

The solution to this problem is seen according to the characterizing part of claim 1 in that one subjecting the raw clay to an acid treatment and the suspension of the acid-treated material in one Hydrocyclone freed from the coarse fractions

Clay minerals which can be purified by the method according to the invention include e.g. B. those of the structural type of swellable smectites, montmorines and montmoriilonoids and clay minerals with species disorder (mixed layer silicates). A summary of these minerals can be found in "Ulimann's Encyclopedia of Industrial Chemistry", Volume 17, 1966, pages 583 to 597.

The method according to the invention is preferably based on a suspension of a clay Montmorillonite-Beidellite series, preferably from bentonite. Bentonites can have varying amounts of Contains alkali or alkaline earth. While the American bentonites of the Wyoming type by a high If they are characterized by alkaline content, the European bentonites contain more exchangeable calcium, which is why they are sometimes subjected to an alkali treatment to increase their swelling capacity. as These alkaline-activated bentonites can also be used as starting materials

The acid treatment of the raw clay is generally known and is used for the production of bleaching earth used on a large scale ("Ulimann's Encyclopedia of Technical Chemistry", Vol. 4, 1953, pp. 541 f.). For practically all acids can be used for the digestion, especially mineral acids, such as hydrochloric acid, Sulfuric acid, nitric acid and phosphoric acid, but also organic acids such as acetic acid. the Acid treatment is generally carried out in a dilute, aqueous suspension. But you can also carry out a so-called "dry digestion" by concentrating the clay with a relatively high concentration Kneads acids.

The clay can also be treated with gaseous acids such as hydrogen chloride or sulfur dioxide will. The acid treatment is usually carried out at elevated temperatures.

In the method according to the invention, the acid treatment is preferably with a mineral acid, such as hydrochloric acid or sulfuric acid at elevated temperatures, preferably at about 90 to 100 ° C or also carried out under pressure.

The duration of the acid treatment depends on the type and concentration of acid as well as on the Temperature.

The acid treatment of the bentonite suspension prevents the clay minerals from gelling in the event of an additional crushing effect of the active substance. The gangue (accompanying minerals) goes through the process mostly without any crushing effect. In general, the acid treatment is carried out until a specific surface area of the clay according to BET of at least 150 g / m ^{2 is} reached. The output eton has a specific surface area of about 60-80 g / m ² . Furthermore, the acid-treated clay generally has a micropore volume of less than 800 Λ of at least 0.13 ml / g and less than 140 Å of at least 0.10 ml / g. In addition, at least 18% by weight of the Al2O3 and Fe2O3 content should have been dissolved out, and at least 12% by weight of hydrated H silicic acid (soluble in soda) should be present.

The acid-treated clay suspension can be poured directly into the hydrocyclone. Preferably however, the acid-treated clay will remove excess acid prior to treatment in the hydrocyclone and soluble salts. This is expediently done by filtering the clay suspension and then filtering it Wash out. Troublesome salts are especially the iron salts, which are sometimes when washed out with water hydrolyze. For this reason it is often advisable to wash with dilute acid until no more iron can be found in the washing water. The remains of the acid can then washed out with water. Residual amounts of iron salts can also be washed out with dilute solutions of complexing agents can be removed. Then the washed-.e material for the Hydrocyclone treatment resuspended in water.

In the hydrocyclone is pref ise a suspension with a solids content of about 150 to i ^r> 250 g / liter, preferably from 180 to 200 g / liter, is used

The mode of action of the hydrocyclone is generally known. For example, »Ullmanns Encyclopedia of Technical Chemistry, Volume 2, Process Engineering I (1972), pages 208 and 220 to 223 referenced.

For the separation of the coarse fractions from clay suspensions, hydrocyclones are used, which according to the desired Limit grain diameters are designed, used. 4>

For acid-treated bentonite suspensions, a limiting particle diameter of 15-20 μm is generally used sufficient for most purposes. The limit grain diameter is understood to mean that in the finely divided cyclone overflow with 100% separating wire-> o contain no particles larger than 15-20μηι are. This corresponds approximately to a cyclone with a diameter of 40 mm and an inlet slot nozzle of approximately 3 χ 10 mm. The pump pressure is around 2 to 5 bar.

The method according to the invention is generally ">"> nen carried out so that the acid-treated bentonite suspension over several series-connected Cyclone stages is pumped, whereby the required separation limit can be doubled for the first stage. Such cyclones have an inside diameter of about 80 mm and are about 1.5 to 3.5 bar Pump pressure operated. This first cleaning stage removes around 10% coarse particles. Of the Cyclone passage has a grain fineness of about 95% smaller than 32 μm. n>

In the second stage, a cyclone fine material with a grain fineness of up to 99% finer 25 μm is obtained, the yield at this stage being about 55% so that the overall yield is generally between 45% and 55% lies

Dividing the process into two steps also has the advantage that the cyclone run (Grobantesle) the second stage can optionally be obtained as an independent product, for Example as fast-filtering fuller's earth.

The suspension obtained from the hydrocyclone fine particles can be worked up in a conventional manner, for example by passing the solid particles through Filtration or centrifugation can be separated from the liquid. The moist cake can then be added be dried at moderate temperatures. That obtained from the suspension of the acid-treated bentonite Product is very suitable as an adsorbent and bleaching agent for the refining of oils and fats as well as solvents, as a filler for paper, plastic, rubber, etc., and also as a paper coating agent as well as for the production of catalysts and carrier material for catalysts. Particularly Due to its small grain size and homogeneity, the product is suitable as a color developer for carbonless copy material. These color developers are used as coating compositions on paper or typewriter tapes Applied on another sheet of paper is sirh, enclosed in microcapsules, an oil solution of a leuco dye. Will the Microcapsules when hit by typewriters or when a ballpoint pen is pressed destroyed, the released leuco dye reacts with the color developer.

Finally, the acid-treated material freed from the coarse fractions can again be treated with alkali or Alkaline earth ions are charged. But you get In this case, as a rule, it is no longer the starting material, as the acid treatment also results in the trivalent ones Ions or a part of it was dissolved out and the crystal lattice due to this treatment a certain Has undergone change.

The products loaded again with alkali or alkaline earth ions are with regard to their particle size with comparable to acid-treated products; but they also have the surprising property that they act as ion exchangers and complexing agents. The loading with alkali or alkaline earth ions takes place in the generally in that the acid-treated products in solutions of alkali or alkaline earth salts or hydroxides are heated. When using salts, alkaline solutions of Salts such as sodium carbonate or sodium borate are preferred.

The invention is illustrated in a non-limiting manner by the following examples:

example 1

Bentonitic raw clay from the Bavarian deposits in the Moosburg-Mainburg-Landshut area is made with about 1000 meq hydrochloric acid, based on 100 g dry clay, and 8 hours at about 95 ° C heated. The dissolved fractions are removed from the solid together with the excess acid severed. The acid-treated clay is washed out to a pH of about 3.5-5.

The still moist material is made into a suspension with a solids content by adding water of about 200 g / liter. The suspension is passed through two hydrocyclone stages and from the Coarse fractions over 25 μιτι, which are usually made of quartz,

Consist of mica, feldspar, pyrite and hematite, largely exempted

Compared to the acid treated feed, those obtained after the second hydrocyclone stage had Fines from the overflow have the following properties

Input material

Fines

Solids content, g / liter 186

Yield,% 100

Specific surface, m'Vg 221

Whiteness (Elrepho), % 72.9

Wet sieving, residue larger, 21.0
25μπτ,%

109
49.5
262
76.7
0.9

The sludge with the fine particles is filtered, and the filter cake obtained is dried and ground at moderate temperatures.

For comparison, a Wyoming type bentonite suspension not treated with acid was used for enrichment of the fines subjected to a hydrocyclone treatment, the solids content of the suspension at most 30 g / liter. The percentage of fines in the starting material or in the hydrocyclone fines (Particles smaller than 25 μπι) is below depending on the solids content of the respective Suspension indicated.

Solids content Fines

d. Suspension (montmorillonite)

i. Starting mat

g / liter%

Fines
(Montmorillonite; d. Hydrocyclone fine material

82.5

86.0
874
91.0

It can therefore be seen that the enrichment effect in the hydrocyclone drops significantly at a solids content of the suspension of 30 g / liter
The viscosity of suspensions of the bentonitic raw clay and of the acid-treated clay obtained by the above procedure was also determined. A rotational viscometer from Haake, type Roto-Visco RV 11 with a rotating body MV I was used for the measurements. The measurements were carried out with a shear gradient of D = 63 (sec- ') and D = 570 (sec-') get the following results:

material Sample no. 2 3 4th 5 6th 1 acidic Raw clay acidic Raw clay acidic Raw clay volume volume volume 31 19th 19th 14th 14th Solids content,% 31 3.7 7.3 3.7 7.3 3.7 PH value 7.3 Viscosity, (mPas) 51 35 4th 12th 3.1 at D 63 see- ' 316 36 8th 4th 4th 3.4 at D 570 see- ' 88

Mac clearly recognizes the drop in viscosity and the reduction in typical thixotropic behavior of bentonite suspensions after acid treatment.

If one takes into account the fact that about 15% ineffective substance due to the acid treatment are dissolved out, then the effectiveness would have to be a raw clay suspension with z. B. 20% solids can be compared with an acid-treated suspension of only 17% solids content. The in the described The decrease in viscosity that occurs under certain conditions is therefore (values determined graphically at D = 570see- ') taking into account the viscosity of pure water at 20 ° C of 0.4 mPas:

for raw clay suspension with 30% solids content: 76%
for raw clay suspension with 20% solids content: 63%

There were also suspensions of the acid-treated clay with a solids content of about 20 wt .-% (pH about 3.7) adjusted to certain pH values by adding alkali or acid, and the viscosities these suspensions were sheared in the manner indicated above D -570see- 'determined. It became the following Get results:

Sample no. PH value viscosity mPa · s 1 10.0 13.0 2 6.9 43 3 3.7 4.3 4th 1.8 6.3

It follows from this that the most favorable pH value is in the weakly acidic range.

Example 2

The raw clay pretreated as in Example t is used as a hot, acidic suspension, as in the Acid treatment occurs, with 2.0 bar in an acid-proof Hydrocyclone passed and largely freed from the coarse fractions over 35 μπι.

Compared to the acid-treated starting material after the hydrocyclone treatment and subsequent filtration and washing, the fine material has a significantly improved adsorptive power, as the following table shows:

The results show the increase in the bleaching effect of the fines content.

Solids content, g / liter yield,%

Bleaching effect with linseed oil *) Loväbond values,

1Ox red + yellow residue> 33 μιτι,%

*) The bleaching activity was measured by treatment of linseed oil with i '% bleaching earth over a period of 30 minutes at 95 ⁼ C in a S' / V 'Cuvette The Lovibondiahl (10 χ red + yellow) of the unbleached linseed oil was 181st

Acid treated
Source material cyclone
fine 214
100 196
88.4 89
14.0 72
6.9

Claims (9)

Patent claims: 1. A method for cleaning clay suspensions with a high solids content, characterized in, that the raw clay is subjected to an acid treatment and the suspension of the acid-treated material is freed from the coarse fractions in a hydrocyclone 2. The method according to claim 1, characterized in that one starts from a suspension of a clay of the montmorillonite-beidellite series, preferably bentonite 3. The method of claim 1 or 2, characterized in that one carries out the acid treatment with a mineral acid, preferably with hydrochloric acid or sulfuric acid at elevated temperature, preferably without pressure at about 90 to 100 ⁰ C or under pressure at about 100 to 300 ° C 4. The method according to any one of claims 1 to 3, characterized in that the acid treatment is carried out until the specific surface (BbT) is at least about 150 g / m ³ and the micropore volume is less than 800 Å at least 0.13 ml / g and smaller 140 Å is at least 0.10 ml / g 5. The method according to any one of claims 1 to 4, characterized in that the acid-treated Excess acid and soluble salts are removed from clay before treatment in the hydrocyclone 6. The method according to any one of claims 1 to 5, characterized in that one in the hydrocyclone -.iine suspension with a solids content of about 150 to 250 g / liter, preferably from about 180 to 200 g / liter, is used. 7. The method according to any one of claims 1 to 6, characterized in that the acid-treated Bentonite suspension pumps through at least two cyclone stages connected in series 8. The method according to any one of claims I to 7, characterized in that one of the Acid-treated material freed from coarse fractions is reloaded with alkali or alkaline earth ions 9. Use of the fines of the clay suspensions purified according to one of claims 1 to 8 as Adsorbents and bleaching agents, fillers, paper coating agents, Color developers, catalysts and carriers for catalysts, ion exchangers and Complexing agents. 10